Gritty mix no good for pawpaw seedlings

alexander3_gw(6 Pennsylvania)September 3, 2013

In the spring of 2010 I germinated several paw paw seeds (Asimina triloba). I planted them in clear 3 liter soda bottles, some in the gritty mix, and others in 5-1-1- mix. By the end of the year, the ones in the 5-1-1 mix had grown quite a bit more on average. In 2011, I repotted some of the gritty mix plants in 5-1-1 mix, and they did much better than those that I left in the gritty mix. I left a few in the gritty mix until this week. They looked even worse in 2012 and this year.

Notably, I could never see any roots through the side of the container, though I did see tap roots reaching the bottom. In the 5-1-1 mix, I could see roots at the side of the container by the end of the first season.

I repotted the remaining few this week, and the lateral roots were really sparse. I don't know if it's because few lateral roots ever formed, or if some of them died back. Several of the remaining lateral roots were dead. I planted 2 in 5-1-1 mix, and tossed one that was barely hanging on.

I've had success growing other plants in the gritty mix, including elm and silk tree, as well as several different house plants, so I think I'm making it correctly.

So, I'm not sure why the paw paw roots were so unhappy. Pawpaws are in the magnolid group of dicots, and have thick fleshy roots, with no discernible root hairs. Among fruit growers, pawpaws have a reputation of having some unusual requirements/preferences because of the behavior of the roots.

With that in mind, I'm wondering if anyone else has had poor results growing magnolids (magnolias, avocado, sassafras eg) in the gritty mix?


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greenman28 NorCal 7b/8a

I've found that either I'm no good at re-potting avocados, or avocados are no good at being re-potted. My avocado has always sulked after root-disturbance, even when I think I'm doing things right; and I've seen others kill avocados when re-potting to and from a variety of potting mixes.

My current mix isn't really the Gritty's mostly screened fir bark, uncomposted, with screened Turface and red Scoria (lava rock) - a sort of modification of what JustaGuy (past forum member) had used. In my case, it wasn't the mix to blame, as experimental as it was. I speculate that I simply wasn't maintaining consistent moisture in the upper inches of mix, which led to leaf-loss, lateral root-loss, and slow recovery after re-potting.

This Summer, I've made a concerted effort to really saturate the avocado mix every two days in 90F+ heat. As a result, the plant's vitality has greatly increased....of course, I've also been fertilizing weekly. The avocado is overdue for a re-potting....but it's too late this season.


    Bookmark   September 4, 2013 at 12:42AM
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I start several hundred pawpaws each year, and have experimented with several mixes. I don't have experience with the magnolids you mention. I have grown other plants in Gritty mix--not pawpaws. In my experience, pawpaws need plenty of moisture, and I believe Gritty mix may be just too fast draining for pawpaws. You might have to use a watering regimen almost like a hydroponic setup to make it work. Pawpaws are also very slow starting plants. They are going to be in containers longer than other plants, before planting out to the ground. Any problems created in mixes, watering or fertilizing are going to be magnified.

I have had good success using 5:1:1 for pawpaws. It's slower to drain than Gritty, and because of the high content of pine bark and peat, the pH starts out low, which is important for pawpaws. You should keep the pH under 5.6 for pawpaws--think blueberries. I have not measured the pH of Gritty, but perhaps it is on the high side. Have you tested the pH and alkalinity of your water?

Pawpaws also seem to be set back more than other plants during potting up.

Another thing I learned recently--in a very costly way--is to avoid sand in the mix. The sand I used had a high limestone content--high pH--and those pawpaws suffered badly.

Good luck,

    Bookmark   September 8, 2013 at 4:37PM
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